In March, two veteran Facebook engineers found themselves grilled about the company's sprawling data collection operations in a hearing for the ongoing lawsuit over the mishandling of private user information stemming from the Cambridge Analytica scandal.

The hearing, a transcript of which was recently unsealed, was aimed at resolving one crucial issue: What information, precisely, does Facebook store about us, and where is it? The engineers' response will come as little relief to those concerned with the company's stewardship of billions of digitized lives: They don't know.

The admissions occurred during a hearing with special master Daniel Garrie, a court-appointed subject-matter expert tasked with resolving a disclosure impasse.